Hybrid energy storage characterization for power profile enhancement in split-shaft wind energy conversion systems

Abstract

This paper characterizes an integrated hybrid energy storage unit required to support the new generator excitation system developed for doubly-fed induction generators in the split-shaft wind energy conversion units. The goal is to improve the power quality while significantly reducing the generator excitation power rating and component counts. The rotor excitation circuit is modified to directly include the storage to its DC link. The output power fluctuation can be attenuated solely by utilizing the rotor-side converter making it self-sufficient from the grid connection. The storage characteristics are identified based on several system design parameters, including the system inertia, inverter capacity, and energy storage capacity. The obtained power generation characteristics suggest an energy storage mix of fast-acting types with a high energy capacity and moderate acting time. A feedback controller is designed to maintain the charge in the storage within the required limits. Adaptive model-predictive control is also developed to reduce power generation fluctuations. The proposed system is investigated and simulated in MATLAB Simulink at different wind speeds to validate the results and demonstrate the system's dynamic performance. It is demonstrated that the system's inertia is critical to damping the high-frequency oscillations of the wind power fluctuations. It is also shown that the bandwidth of the control system is determined by the system inertia and the size of the storage and inverter power rating.